Multi-level pulser and related apparatus and methods

ABSTRACT

Apparatus and methods are provided directed to a device, including at least one ultrasonic transducer, a multi-level pulser coupled to the at least one ultrasonic transducer; the multi-level pulser including a plurality of input terminals configured to receive respective input voltages, an output terminal configured to provide an output voltage, and a signal path between a first input terminal and the output terminal including a first transistor having a first conductivity type coupled to a first diode and, in parallel, a second transistor having a second conductivity type coupled to a second diode.

RELATED APPLICATIONS

This Application is a continuation, claiming the benefit under 35 U.S.C.§ 120, of U.S. patent application Ser. No. 15/288,324, filed Oct. 7,2016, entitled “MULTI-LEVEL PULSER AND RELATED APPARATUS AND METHODS”which is hereby incorporated herein by reference in its entirety.

U.S. patent application Ser. No. 15/288,324 is a continuation, claimingthe benefit under 35 U.S.C. § 120, of U.S. patent application Ser. No.14/957,382, entitled “MULTI-LEVEL PULSER AND RELATED APPARATUS ANDMETHODS” filed on Dec. 2, 2015, which is hereby incorporated herein byreference in its entirety.

BACKGROUND Field

The present application relates to ultrasound devices having amulti-level pulser and/or a level shifter.

Related Art

Ultrasound devices may be used to perform diagnostic imaging and/ortreatment. Ultrasound imaging may be used to see internal soft tissuebody structures. Ultrasound imaging may be used to find a source of adisease or to exclude any pathology. Ultrasound devices use sound waveswith frequencies which are higher than those audible to humans.Ultrasonic images are made by sending pulses of ultrasound into tissueusing a probe. The sound waves are reflected off the tissue, withdifferent tissues reflecting varying degrees of sound. These reflectedsound waves may be recorded and displayed as an image to the operator.The strength (amplitude) of the sound signal and the time it takes forthe wave to travel through the body provide information used to producean image.

Many different types of images can be formed using ultrasound devices.The images can be real-time images. For example, images can be generatedthat show two-dimensional cross-sections of tissue, blood flow, motionof tissue over time, the location of blood, the presence of specificmolecules, the stiffness of tissue, or the anatomy of athree-dimensional region.

SUMMARY

According to aspects of the present application, there are providedapparatus and methods directed to an apparatus, including at least oneultrasonic transducer, a multi-level pulser coupled to the at least oneultrasonic transducer; the multi-level pulser including a plurality ofinput terminals configured to receive respective input voltages, anoutput terminal configured to provide an output voltage, and a signalpath between a first input terminal and the output terminal including afirst transistor having a first conductivity type coupled to a firstdiode and, in parallel, a second transistor having a second conductivitytype coupled to a second diode.

According to aspects of the present application, there are providedapparatus and methods directed to a multi-level pulser, including aplurality of input terminals configured to receive respective inputvoltages, an output terminal configured to provide an output voltage,and a signal path between a first input terminal and the output terminalincluding a transistor having a first conductivity type coupled to afirst diode and, in parallel, a transistor having a second conductivitytype coupled to a second diode.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects and embodiments of the application will be describedwith reference to the following figures. It should be appreciated thatthe figures are not necessarily drawn to scale. Items appearing inmultiple figures are indicated by the same reference number in all thefigures in which they appear.

FIG. 1 is a block diagram of an ultrasound device including amulti-level pulser and/or a level shifter, according to a non-limitingembodiment of the present application.

FIG. 2 illustrates a non-limiting circuit diagram of a multi-levelpulser, according to a non-limiting embodiment of the presentapplication.

FIG. 3A illustrates a circuit diagram of a first embodiment of a levelshifter, according to a non-limiting embodiment of the presentapplication.

FIG. 3B illustrates a circuit diagram of a second embodiment of a levelshifter, according to a non-limiting embodiment of the presentapplication.

FIG. 4A illustrates a non-limiting equivalent circuit of the circuit ofFIG. 2, during a first phase of a multi-level pulse formation, accordingto a non-limiting embodiment of the present application.

FIG. 4B illustrates a non-limiting equivalent circuit of the circuit ofFIG. 2, during a second phase of a multi-level pulse formation,according to a non-limiting embodiment of the present application.

FIG. 4C illustrates a non-limiting equivalent circuit of the circuit ofFIG. 2, during a third phase of a multi-level pulse formation, accordingto a non-limiting embodiment of the present application.

FIG. 4D illustrates a non-limiting equivalent circuit of the circuit ofFIG. 2, during a fourth phase of a multi-level pulse formation,according to a non-limiting embodiment of the present application.

FIG. 4E illustrates a non-limiting equivalent circuit of the circuit ofFIG. 2, during a fifth phase of a multi-level pulse formation, accordingto a non-limiting embodiment of the present application.

FIG. 4F illustrates a non-limiting equivalent circuit of the circuit ofFIG. 2, during a sixth phase of a multi-level pulse formation, accordingto a non-limiting embodiment of the present application.

FIG. 5 is a graph illustrating a non-limiting example of atime-dependent multi-level pulse and the control signals, according to anon-limiting embodiment of the present application.

DETAILED DESCRIPTION

The inventors have recognized and appreciated that the power necessaryto transmit high-intensity pulses may be greatly decreased by formingelectric pulses having multiple levels.

Aspects of the present application relate to high-intensity focusedultrasound (HIFU) procedures that may be used to focus high-intensityultrasound energy on targets to treat diseases or damaged tissues byselectively increasing the temperature of the target or the regionsurrounding the target. HIFU procedures may be used for therapeutic orablative purposes. Pulsed signals may be used to generate HIFUs.According to aspects of the present application, the generation of suchhigh-intensity pulses may require driving voltages of several tens toseveral hundreds of volts.

The power consumption associated with the generation of typical 2-levelpulses having a “low” voltage and a “high” voltage is proportional tothe square of the high voltage. For example, the generation of a 2-levelpulse having a “low” voltage equal to 0 requires a power equal to:P ₍₂₎ =C*V ² *f

where P₍₂₎ is the power needed to generate the 2-level pulse, C is thecapacitance of the load receiving the pulse, V is the “high” voltage andf is the repetition frequency of the 2-level pulse.

According to aspects of the present application, the power consumptionassociated with the generation of pulses for HIFU procedures may exceedseveral tens to thousands of watts, thus causing the circuit to generatesignificant amounts of heat.

Aspects of the present application relate to multi-level pulsersdesigned to decrease power consumption and heat dissipation.

Furthermore, aspects of the present application relate to a levelshifter circuit configured to drive the multi-level pulser. The levelshifter disclosed herein may dissipate considerably less power comparedto typical level shifters. Accordingly, power may be dissipated onlywhen a level is switched, while static power consumption may benegligible.

The aspects and embodiments described above, as well as additionalaspects and embodiments, are described further below. These aspectsand/or embodiments may be used individually, all together, or in anycombination of two or more, as the application is not limited in thisrespect.

FIG. 1 illustrates a circuit for processing received ultrasound signals,according to a non-limiting embodiment of the present application. Thecircuit 100 includes N ultrasonic transducers 102 a . . . 102 n, whereinN is an integer. The ultrasonic transducers are sensors in someembodiments, producing electrical signals representing receivedultrasound signals. The ultrasonic transducers may also transmitultrasound signals in some embodiments. The ultrasonic transducers maybe capacitive micromachined ultrasonic transducers (CMUTs) in someembodiments. The ultrasonic transducers may be piezoelectricmicromachined ultrasonic transducers (PMUTs) in some embodiments.Further alternative types of ultrasonic transducers may be used in otherembodiments.

The circuit 100 further comprises N circuitry channels 104 a . . . 104n. The circuitry channels may correspond to a respective ultrasonictransducer 102 a . . . 102 n. For example, there may be eight ultrasonictransducers 102 a . . . 102 n and eight corresponding circuitry channels104 a . . . 104 n. In some embodiments, the number of ultrasonictransducers 102 a . . . 102 n may be greater than the number ofcircuitry channels.

According to aspects of the present application, the circuitry channels104 a . . . 104 n may include transmit circuitry. The transmit circuitrymay include level shifters 106 a . . . 106 n coupled to respectivemulti-level pulsers 108 a . . . 108 n. The multi-level pulsers 108 a . .. 108 n may control the respective ultrasonic transducers 102 a . . .102 n to emit ultrasound signals.

Circuitry channels 104 a . . . 104 n may also include receive circuitry.The receive circuitry of the circuitry channels 104 a . . . 104 n mayreceive the electrical signals output from respective ultrasonictransducers 102 a . . . 102 n. In the illustrated example, eachcircuitry channel 104 a . . . 104 n includes a respective receive switch110 a . . . 110 n and an amplifier 112 a . . . 112 n. The receiveswitches 110 a . . . 110 n may be controlled to activate/deactivatereadout of an electrical signal from a given ultrasonic transducer 102 a. . . 102 n. More generally, the receive switches 110 a . . . 110 n maybe receive circuits, since alternatives to a switch may be employed toperform the same function. The amplifiers 112 a . . . 112 n may betrans-impedance amplifiers (TIAs).

The circuit 100 further comprises an averaging circuit 114, which isalso referred to herein as a summer or a summing amplifier. In someembodiments, the averaging circuit 114 is a buffer or an amplifier. Theaveraging circuit 114 may receive output signals from one or more of theamplifiers 112 a . . . 112 n and may provide an averaged output signal.The averaged output signal may be formed in part by adding orsubtracting the signals from the various amplifiers 112 a . . . 112 n.The averaging circuit 114 may include a variable feedback resistance.The value of the variable feedback resistance may be adjusteddynamically based upon the number of amplifiers 112 a . . . 112 n fromwhich the averaging circuit receives signals. The averaging circuit 114is coupled to an auto-zero block 116.

The auto-zero block 116 is coupled to a time gain compensation circuit118 which includes an attenuator 120 and a fixed gain amplifier 122.Time gain compensation circuit 118 is coupled to an analog-to-digitalconverter (ADC) 126 via ADC drivers 124. In the illustrated example, theADC drivers 124 include a first ADC driver 125 a and a second ADC driver125 b. The ADC 126 digitizes the signal(s) from the averaging circuit114.

While FIG. 1 illustrates a number of components as part of a circuit ofan ultrasound device, it should be appreciated that the various aspectsdescribed herein are not limited to the exact components orconfiguration of components illustrated. For example, aspects of thepresent application relate to the multi-level pulsers 108 a . . . 108 nand the level shifters 106 a . . . 106 n.

The components of FIG. 1 may be located on a single substrate or ondifferent substrates. For example, as illustrated, the ultrasonictransducers 102 a . . . 102 n may be on a first substrate 128 a and theremaining illustrated components may be on a second substrate 128 b. Thefirst and/or second substrates may be semiconductor substrates, such assilicon substrates. In an alternative embodiment, the components of FIG.1 may be on a single substrate. For example, the ultrasonic transducers102 a . . . 102 n and the illustrated circuitry may be monolithicallyintegrated on the same semiconductor die. Such integration may befacilitated by using CMUTs as the ultrasonic transducers.

According to an embodiment, the components of FIG. 1 form part of anultrasound probe. The ultrasound probe may be handheld. In someembodiments, the components of FIG. 1 form part of an ultrasound patchconfigured to be worn by a patient.

FIG. 2 illustrates the circuit diagram of a multi-level pulser,according to aspects to the present application. In some embodiments,multi-level pulser 200 may be configured to transmit a pulse tocapacitor C. Capacitor C may represent the capacitance associated withan ultrasound transducer. For example, capacitor C may represent acapacitive micromachined ultrasonic transducer (CMUT). However,multi-level pulser 200 may be configured to transmit a pulse to aresistor, a resistive network or a network exhibiting any suitablecombination of resistive and reactive elements.

In the non-limiting embodiment illustrated in FIG. 2, multi-level pulser200 is configured to provide an N-level pulse, where N may assume anyvalue greater than 2. The power consumption P_((N)) associated with thetransmission of a N-level pulser to capacitor C is equal to:P _((N)) =C*V ² *f/(N−1)

where f is the repetition frequency of the pulsed waveform. Accordingly,power consumption is reduced by a factor N−1 compared to typical 2-levelpulsers.

In some embodiments, N-level pulser 200 may comprise 2N−2 transistorsand 2N−4 diodes. However, any suitable number of transistors may beused. Among the 2N−2 transistors, N−1 may exhibit one type ofconductivity and N−1 may exhibit the opposite type of conductivity.However any other suitable combination of types of conductivity may beused. For example, N−1 transistors may be nMOS and N−1 transistors maybe pMOS. However any other suitable type of transistor may be used.

N-level pulser 200 may comprise N circuit blocks 201 ₁, 201 ₂ . . . 201_(N). The N circuit blocks may be connected to node 202. One terminal ofcapacitor C may also be connected to node 202. The second terminal ofcapacitor C may be connected to ground. Circuit block 201 ₁ may comprisepMOS transistor T₁, having the source connected to a reference voltageV_(DD) and the drain connected to node 202. Reference voltage V_(DD) maybe a voltage supply. The gate of transistor T₁ may be driven by signalV_(G1).

Circuit block 201 _(N) may comprise nMOS transistor T_(2N−2), having thesource connected to a reference voltage V_(SS) and the drain connectedto node 202. In some embodiments, reference voltage V_(SS) may be lessthan reference voltage V_(DD). However, pulser 200 is not limited inthis respect. Furthermore, reference voltage V_(SS) may positive,negative or equal to zero. The gate of transistor T_(2N−2) may be drivenby signal V_(G2N−2).

In some embodiments, circuit blocks 201 ₂ may comprise two transistorsT₂ and T₃ and two diodes D₂ and D₃. Transistor T₂ and diode D₂ may beconnected in series and transistor T₃ and diode D₃ may also be connectedin series. The two series may be connected in parallel. In someembodiments, T₂ may be a pMOS transistor, having the source connected tothe reference voltage V_(MID2) and the drain connected to the anode ofD₂ and T₃ may be an nMOS transistor, having the source connected toV_(MID2) and the drain connected to the cathode of D₃. In someembodiments, V_(MID2) may be greater than V_(SS) and less than V_(DD).The cathode of D₂ and the anode of D₃ may be connected to node 202.Furthermore, the gate of T₂ may be driven by signal V_(G2) and the gateof T₃ may be driven by signal V_(G3).

In some embodiments, circuit blocks 201 _(i), where i may assume anyvalue between 3 and N−1, may comprise two transistors T_(2i−2) andT_(2i−1) and two diodes D_(2i−2) and D_(2i−1). Transistor T_(2i−2) anddiode D_(2i−2) may be connected in series and transistor T_(2i−1) anddiode D_(2i−1) may also be connected in series. The two series may beconnected in parallel. In some embodiments, T_(2i−2) may be a pMOStransistor, having the source connected to the reference voltageV_(MIDi) and the drain connected to the anode of D_(2i−2) and T_(2i−1)may be an nMOS transistor, having the source connected to V_(MIDi) andthe drain connected to the cathode of D_(2i−1). In some embodiments,V_(MIDi) may be greater than V_(SS) and less than V_(MID2). The cathodeof D_(2i−2) and the anode of D_(2i−1) may be connected to node 202.Furthermore, the gate of T_(2i−2) may be driven by signal V_(G2i−2) andthe gate of T_(2i−1) may be driven by signal V_(G2i−1).

V_(DD), V_(SS) and V_(MIDi), for any value of i, may have values betweenapproximately −300V and 300V, between approximately −200V and 200V, orany suitable value or range of values. Other values are also possible.

FIG. 3A and FIG. 3B illustrate two non-limiting embodiments of a levelshifter circuit, according to aspects of the present application. Insome embodiments, level shifter 301, shown in FIG. 3A, may be integratedon the same chip as pulser 200. In some embodiments, level shifter 301may be used to drive any of the pMOS transistors of pulser 200. Forexample, level shifter 301 may be used to output signal V_(G2i−2) todrive the gate of transistor T_(2i−2). The input voltage V_(IN2i−2) tolevel shifter 301 may be a control signal having two possible voltagelevels: V_(SS) and V_(SS)+δV, where δV may assume any suitable value orrange of values. In some embodiments, control signal V_(IN2i−2) may begenerated by a circuit integrated on the same chip as level shifter 301.However, control signal V_(IN2i−2) may also be generated by a circuitintegrated on a separate chip. In some embodiments, level shifter 301may comprise an inverter I_(M1), followed by capacitor C_(M). The powersupply pins of inverter I_(M1) may be connected to voltages V_(SS) andV_(SS)+δV. Capacitor C_(M) may be followed by the series of a number ofinverters. In some embodiments, capacitor C_(M) is followed by threeinverters I_(M2), I_(M3) and I_(M4). The “−” and “+” power supply pinsof inverter I_(M2), I_(M3) and I_(M4) may be connected to voltagesV_(MIDi)−ΔV and V_(MIDi) respectively. In some non-limiting embodiments,level shifter 301 may comprise diode D_(M). The cathode or diode D_(M)may be connected to the output of capacitor C_(M), while the anode maybe connected to the V_(MIDi)−ΔV rail. While level shifter 301 comprisesfour inverters in the non-limiting embodiment of FIG. 3A, any suitablenumber of inverters may otherwise be used. Output voltage V_(G2i−2) mayassume two possible voltages: V_(MIDi)−ΔV and V_(MIDi).

In some embodiments, level shifter 302, shown in FIG. 3B, may beintegrated on the same chip as pulser 200. In some embodiments, levelshifter 302 may be used to drive any of the nMOS transistors of pulser200. For example, level shifter 302 may be used to output signalV_(G2i−1) to drive the gate of transistor T_(2i−1). The input voltageV_(IN2i−1) to level shifter 302 may be a control signal having twopossible voltage levels: V_(SS) and V_(SS)+δV. In some embodiments,control signal V_(IN2i−1) may be generated by a circuit integrated onthe same chip as level shifter 302. However, control signal V_(IN2i−1)may also be generated by a circuit integrated on a separate chip. Insome embodiments, level shifter 302 may comprise an inverter I_(P1),followed by capacitor C_(P). The power supply pins of inverter I_(P1)may be connected to voltages V_(SS) and V_(SS)+δV. Capacitor C_(P) maybe followed by the series of a number of inverters. In some embodiments,capacitor C_(P) is followed by two inverters I_(P2) and I_(P3) The powersupply pins of inverter I_(M2) and I_(M3) may be connected to voltagesV_(MIDi) and V_(MIDi)+ΔV. In some non-limiting embodiments, levelshifter 302 may comprise diode DP. The cathode or diode D_(P) may beconnected to the output of capacitor C_(P), while the anode may beconnected to the V_(MIDi) rail. While level shifter 302 comprises threeinverters in the non-limiting embodiment of FIG. 3B, any suitable numberof inverters may otherwise be used. Output voltage V_(G2i−i) may assumetwo possible voltages: V_(MIDi) and V_(MIDi)+ΔV.

According to aspects of the present application, level shifters 301 and302 may dissipate power only when a level is switched, while staticpower may be negligible. Capacitors C_(M) and C_(P) may be used to shiftthe voltage level by storing a constant voltage drop across them. Forexample, the static power consumption may be less than 100 mW, less than1 mW, less than 1 μW or less than any suitable value.

FIG. 4A, FIG. 4B, FIG. 4C, FIG. 4D, FIG. 4E, and FIG. 4F illustrate sixsnapshots of pulser 200 corresponding to the six phases associated withthe formation of a 4-level pulse, according to aspects on the presentapplication. In the figures, only the active blocks are shown. While inthe non-limiting example N is equal to 4, any other suitable value of N,such that N is greater than 2, may otherwise be used. In the example,V_(SS) is set to 0.

FIG. 5 illustrates a non-limiting example of multi-level pulse 500generated according to aspects of the present application. In thenon-limiting example, pulse 500 exhibits 4 levels: 0, V_(MID3),V_(MID2), and V_(DD). In addition, FIG. 5 illustrates the 6 controlsignals V_(G1), V_(G2), V_(G3), V_(G4), V_(G5), and V_(G6) used torespectively drive the gates of transistors T₁, T₂, T₃, T₄, T₅, and T₆.The process associated with the pulse generation can be divided in 6phases. Between t₁ and t₂, pulse 500 may be increased from 0 to V_(MID3)by providing a negative pulse 504 to transistor T₄ through V_(G4) asshown in FIG. 5. FIG. 4A illustrates pulser 201 between t₁ and t₂.During this period, the gate of transistor T₄ may be driven by a voltageequal to V_(MID3)−ΔV. ΔV may be chosen so as to create a conductivechannel and cause transistor T₄ to drive a current between the sourceand the drain passing through diode D₄. Such current may chargecapacitor C, such that an output voltage of V_(MID3) is obtained,neglecting any voltage drop on T₄ and D₄. Pulse 504 may be obtainedthrough level shifter 301.

Between t₂ and t₃, pulse 500 may be increased from V_(MID3) to V_(MID2)by providing a negative pulse 502 to transistor T₂ through V_(G2) asshown in FIG. 5. FIG. 4B illustrates pulser 201 between t₂ and t₃.During this period, the gate of transistor T₂ may be driven by a voltageequal to V_(MID2)−ΔV. ΔV may be chosen so as to create a conductivechannel and cause transistor T₂ to drive a current between the sourceand the drain passing through diode D₂. Such current may chargecapacitor C, such that an output voltage of V_(MID2) is obtained,neglecting any voltage drop on T₂ and D₂. Pulse 502 may be obtainedthrough level shifter 301.

Between t₃ and t₄, pulse 500 may be increased from V_(MID2) to V_(DD) byproviding a negative pulse 501 to transistor T₁ through V_(G1) as shownin FIG. 5. FIG. 4C illustrates pulser 201 between t₃ and t₄. During thisperiod, the gate of transistor T₁ may be driven by a voltage equal toV_(DD)−ΔV may be chosen so as to create a conductive channel and causetransistor T₁ to drive a current between the source and the drain. Suchcurrent may charge capacitor C, such that an output voltage of V_(DD) isobtained, neglecting any voltage drop on T₁. Pulse 501 may be obtainedthrough level shifter 301.

Between t₄ and t₅, pulse 500 may be decreased from V_(DD) to V_(MID2) byproviding a positive pulse 503 to transistor T₃ through V_(G3) as shownin FIG. 5. FIG. 4D illustrates pulser 201 between t₄ and t₅. During thisperiod, the gate of transistor T₃ may be driven by a voltage equal toV_(MID2)+ΔV. ΔV may be chosen so as to create a conductive channel andcause transistor T₃ to drive a current between the drain and the source.Such current may discharge capacitor C, such that an output voltage ofV_(MID2) is obtained, neglecting any voltage drop on T₃ and D₃. Pulse503 may be obtained through level shifter 302.

Between t₅ and t₆, pulse 500 may be decreased from V_(MID2) to V_(MID3)by providing a positive pulse 505 to transistor T₅ through V_(G5) asshown in FIG. 5. FIG. 4E illustrates pulser 201 between t₅ and t₆.During this period, the gate of transistor T₅ may be driven by a voltageequal to V_(MID3)+ΔV. ΔV may be chosen so as to create a conductivechannel and cause transistor T₅ to drive a current between the drain andthe source. Such current may discharge capacitor C, such that an outputvoltage of V_(MID3) is obtained, neglecting any voltage drop on T₅ andD₅. Pulse 505 may be obtained through level shifter 302.

After t₆, pulse 500 may be decreased from V_(MID3) to 0 by providing apositive pulse 506 to transistor T₆ through V_(G6) as shown in FIG. 5.FIG. 4F illustrates pulser 201 after t₆. During this period, the gate oftransistor T₆ may be driven by a voltage equal to ΔV. ΔV may be chosenso as to create a conductive channel and cause transistor T₆ to drive acurrent between the drain and the source. Such current may dischargecapacitor C, such that an output voltage of 0 is obtained, neglectingany voltage drop on T₆. Pulse 506 may be obtained through level shifter302.

In the non-limiting example in connection to FIG. 5, pulse 500 isunipolar. However, multi-level pulser 200 in not limited in thisrespect. Multi-level pulser 200 may alternatively be configured totransmit bipolar pulses exhibiting levels having positive and negativevoltages. In accordance with another aspect of the present application,the multi-level pulser 200 may be considered a multi-level chargerecycling waveform generator in that charge recycling occurs on thedecrementing step as charge is transferred from the output capacitanceback into the power supply. In accordance with another aspect of thepresent application, although the multi-level pulser has been describedas being used to drive a capacitive output, it may also be used to drivea resistive output.

The amount of power saving when using a level shifter of the typesdescribed herein may be significant. In some embodiments, utilizing alevel shifter of the types described herein may provide substantialpower saving by setting the static power consumption to approximatelyzero. Accordingly, power may be dissipated only during switching states.

Having thus described several aspects and embodiments of the technologyof this application, it is to be appreciated that various alterations,modifications, and improvements will readily occur to those of ordinaryskill in the art. Such alterations, modifications, and improvements areintended to be within the spirit and scope of the technology describedin the application. It is, therefore, to be understood that theforegoing embodiments are presented by way of example only and that,within the scope of the appended claims and equivalents thereto,inventive embodiments may be practiced otherwise than as specificallydescribed.

As described, some aspects may be embodied as one or more methods. Theacts performed as part of the method(s) may be ordered in any suitableway. Accordingly, embodiments may be constructed in which acts areperformed in an order different than illustrated, which may includeperforming some acts simultaneously, even though shown as sequentialacts in illustrative embodiments.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements.

As used herein, the term “between” used in a numerical context is to beinclusive unless indicated otherwise. For example, “between A and B”includes A and B unless indicated otherwise.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively.

What is claimed is:
 1. An apparatus, comprising: at least one ultrasonictransducer on a first substrate; and a multi-level pulser on a secondsubstrate coupled to the at least one ultrasonic transducer, wherein thefirst substrate and the second substrate are different substrates, themulti-level pulser including: a plurality of input terminals configuredto receive respective input voltages; an output terminal configured toprovide an output voltage; and a signal path between a first inputterminal of the plurality of input terminals and the output terminalincluding a first transistor coupled to a first diode and, in parallel,a second transistor coupled to a second diode, wherein the firsttransistor is either a pMOS transistor or an nMOS transistor and thesecond transistor is an NMOS transistor if the first transistor is apMOS transistor or a pMOS transistor if the first transistor is an nMOStransistor.
 2. The apparatus of claim 1, further comprising a controllerconfigured to control a charge and discharge of an output capacitanceassociated with the ultrasonic transducer so as to provide chargerecycling.
 3. The apparatus of claim 1, wherein the multi-level pulsercomprises a plurality of signal paths between respective input terminalsof the plurality of input terminals and the output terminal, each signalpath including a pMOS or nMOS transistor coupled to a first diode and,in parallel, a pMOS or nMOS transistor coupled to a second diode,wherein the pMOS or nMOS transistor coupled to the second diode is annMOS transistor when the pMOS or nMOS transistor coupled to the firstdiode is a pMOS transistor, and wherein the pMOS or nMOS transistorcoupled to the second diode is a pMOS transistor when the pMOS or nMOStransistor coupled to the first diode is an nMOS transistor.
 4. Theapparatus of claim 1, wherein the output voltage is equal to apredetermined input voltage.
 5. The apparatus of claim 1, furthercomprising a capacitor coupled to the output terminal.
 6. The apparatusof claim 1, further comprising a resistor coupled to the outputterminal.
 7. The apparatus of claim 1, wherein the first transistor ispMOS and the second transistor is nMOS.
 8. The apparatus of claim 1,wherein the first diode has an anode connected to the first transistorand a cathode connected to the output terminal.
 9. The apparatus ofclaim 1, wherein the second diode has a cathode connected to the secondtransistor and an anode connected to the output terminal.
 10. Anapparatus, comprising: at least one ultrasonic transducer on a firstsubstrate, and a level shifter on a second substrate coupled to the atleast one ultrasonic transducer, wherein the first substrate and thesecond substrate are different substrates, the level shifter including:an input terminal configured to receive an input voltage; an outputterminal configured to provide an output voltage level-shifted from theinput voltage; a capacitor coupled between the input terminal and theoutput terminal; and a diode coupled in a reverse-biased configurationbetween an input to an active high voltage element and a first voltageof a high voltage power supply; wherein the input of the active highvoltage element is coupled to an output of the capacitor.
 11. Theapparatus of claim 10, wherein the first substrate is a semiconductorsubstrate.
 12. The apparatus of claim 10, wherein the at least oneultrasonic transducer is a capacitive micromachined ultrasonictransducer (CMUT).
 13. The apparatus of claim 10, further comprising apulser on the second substrate and coupled to the level shifter.
 14. Theapparatus of claim 10, comprising a plurality of ultrasonic transducersincluding the at least one ultrasonic transducer, wherein the pluralityof ultrasonic transducer are configured to apply high intensity focusedultrasound (HIFU).